1. Field of the Invention
The present invention relates to determining the level of a fluid in a well such as an oil well or water well.
2. Description of the Art Practices
It is known that wells replenish fluid at different rates even in the same formation or well field. The maximum production from a given well occurs when the fluid level in the well bore is as low as possible compared to the level in the surrounding formation. The rate of fluid flow into the well bore (production) is maximized then because the hydrostatic head driving the fluid is at a maximum.
The preceding observation suggests that the well pump should run constantly to keep the level in the well bore as low as possible thus maximizing production. Of course, this is unsatisfactory for several reasons.
First, running the pump constantly or at too great a speed is inefficient since, some of the time, the well bore is completely empty and there is nothing to pump. Thus energy conservation becomes a cost consideration. Second, the equipment is subject to wear and damage resulting in costly repairs when pumps are run dry. Third, paraffin build up is more pronounced when a well is allowed to pump dry. In the dry pump condition gases are drawn into the bore. The gases in the bore then expand and cool. As the gases cool, paraffin build up is promoted as these high melting hydrocarbons begin to plate out on the surfaces of the bore.
Given the above considerations, control strategies aimed at optimizing well production have emerged. Notably, timers have been used to control the pump duty cycle. A timer may be programmed to run the well nearly perfectly if the one could determine the duration of the on cycle and off cycle which keeps the fluid level in the bore low but which does not pump the bore dry, and if steady conditions in the bore and with the equipment prevail.
The pump on cycle and off cycle can be determined for a group of wells or for an entire well field. Savings in energy may be maximized by knowing which wells fill at what rate and then optimizing pumping to reduce or maintain a constant electric load below the maximum peak available.
Given fluid level information, deciding when or how fast to run the pump is very straight forward and production can be optimized. Fluid level determinations, particularly for deep down hole (bore) systems, have been implemented. Unfortunately, these deep down hole have been costly and complex to install, unreliable in operation, and costly to repair or service. Although the implementation details will not be discussed here, it is worth noting that these systems, when operating correctly, have proven that significant gains in well production are available when control strategies using fluid level measurement are applied.
Clearly, what is needed is a control system with the advantages of fluid level measurement which is cost effective to install and operate and which is reliable. Basic features for fluid level measurement should include applicability to oil, water, or other wells and should be applicable to rod, screw, or other pump types.
A fluid level measurement system should be simple and inexpensive to install in the T-Head and useful for well depths to 10,000 feet. Such a fluid level measurement system should be self calibrating for each installation and accurate to 10 feet (3.1 meters) and robust to harsh environments within and around the well.